Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

The published paper associated with this dataset is: Relationships Between Plankton Size Spectra, Net Primary Production, and the Biological Carbon Pump.

Stukel, M. R., Décima, M., Kelly, T. B., Landry, M. R., Nodder, S. D., Ohman, M. D., Selph, K. E., & Yingling, N. (2024). Relationships Between Plankton Size Spectra, Net Primary Production, and the Biological Carbon Pump. Global Biogeochemical Cycles, 38(4). Portico. https://doi.org/10.1029/2023gb007994

In situ data were compiled from five field programs: CCE LTER, CRD FluZIE, BLOOFINZ-GoM, SalpPOOP, and HOT (Fig.1 illustrates their locations, Stukel et al, 2024). Datasets from the California Current Ecosystem Long-Term Ecological Research (CCE LTER) Program are derived from eight cruises spanning multiple seasons and years (2006-2016) in the southern sector of the California Current System.  This region includes a productivity gradient stretching from a coastal upwelling biome to an oligotrophic offshore domain (Ohman et al. 2013).  Results from the Costa Rica Dome (CRD) are derived from the CRD FLUxes and ZInc Experiments (FLUZIE) cruise in an open-ocean upwelling region of the Eastern Tropical Pacific in July 2010 (Landry et al. 2016).  The Gulf of Mexico (GoM) dataset was collected on two cruises of the Bluefin Larvae in Oligotrophic Ocean Foodwebs, Investigations of Nutrients to Zooplankton (BLOOFINZ-GoM) program in May 2017 and May 2018 that focused on the oligotrophic deepwater spawning grounds of Atlantic Bluefin Tuna (Gerard et al. 2022).  The Salp Particle expOrt and Oceanic Production (SalpPOOP) Expedition investigated the Southern Ocean region near the Subtropical Front and sampled waters of frontal, subtropical and subantarctic origin (Décima et al. 2023).  All of these programs utilized quasi-Lagrangian sampling schemes with Lagrangian experiments that lasted from ~2.25 to ~7.75 days in duration (typical duration = 4.25 days) allowing repeated sampling of plankton communities from bacteria to microzooplankton within distinct water parcels (Landry 2009).  Samples from the North Pacific Subtropical Gyre were collected by the Hawaii Ocean Time-series program, which samples the time-series station ALOHA over ~3 days near Hawai’i with ~monthly frequency (Church et al. 2013; Karl and Church 2014).  Brief descriptions of field methods are given below.  Additional details are available in original publications as cited. 

Microbes – Samples for microbial biomass were collected by Niskin bottles at 6 – 8 depths spanning the euphotic zone.  Picoplankton abundances (heterotrophic bacteria, Prochlorococcus, Synechococcus, and picoeukaryotes) were determined by flow cytometry and converted to biomass using carbon cell-1 conversion factors for their respective regions as determined by the original investigators (Selph et al. 2016; Selph et al. 2021). While conversion factors did vary slightly between regions for some groups, they were generally quite similar.  Nano- and microplankton biomasses were determined by epifluorescence microscopy with proflavin (protein) and DAPI (nucleic acid) staining (Taylor et al. 2012; Taylor et al. 2016).  50-mL samples were filtered through 0.8-µm filters to quantify ~2- to 12-µm cells (imaged at 60X or 63X magnification) and 450-mL samples were filtered through 8.0-µm filters to quantify >12-µm cells (imaged at 20X magnification).  Cells were manually outlined based on proflavin fluorescence and carbon biomass was determined from biovolume using equations in Menden-Deuer and Lessard (2000).  We note that while this approach will accurately quantify most nano- and micro-sized protists (autotrophic, heterotrophic, and mixotrophic), some fragile taxa (e.g., some ciliates) may not survive preservation and hence could be undercounted. 

Mesozooplankton – Mesozooplankton were collected with either a ring net or a bongo net with 202-µm mesh, equipped with a General Oceanics flow meter and a depth sensor.  Double oblique net tows (to a maximum depth between 100 and 210 m) were conducted twice daily (paired day and night tows) during Lagrangian experiments.  Typically three day/night pairs of tows were conducted for each occupation of Station ALOHA in the subtropical North Pacific.  After recovery, samples were split using a Folsom splitter and sequentially filtered through nested sieves (5 mm, 2 mm, 1 mm, 0.5 mm, 0.2 mm).  Sieves were rinsed onto pre-weighed, 47-mm diameter, 0.2-mm mesh filters, rinsed with isotonic ammonium formate, and dried for storage (Décima et al. 2016; Landry and Swalethorp 2021).  On land, samples were weighed to determine dry mass.  Filters from most projects were then subsampled for C/N analyses by elemental analyzer thus providing carbon values for all 5 size classes.  For cruises without direct carbon measurements available, dry weight was converted to carbon using equations in Landry et al. (2001).  On the SalpPOOP cruise, >5-mm salps were removed from the >5-mm sample and individually sized (for all other cruises, no organisms were removed from the large size fraction and it was treated identically to other size fractions).  We estimated salp biomass using allometric relationships in Iguchi et al. (2004) and included it to the >5-mm sample.  

Data treatment  We compiled flow cytometry, epifluorescence microscopy, and zooplankton net tow data to compute size spectra.  Our choice of size bins was dictated by the size bins reported by each field program, which typically followed approximately octave (base 2) scaling.  However, we were forced to make some distinct choices:  I) Cell size was not reported for flow cytometry data, hence we assumed that the size bin for picoplankton was 0.5 – 2.0 µm.  This is likely a reasonable range that encompasses most biomass for populations including heterotrophic bacteria, Prochlorococcus, Synechococcus, and picoeukaryotes.  II) The largest size class of microplankton reported from epifluorescence microscopy data was typically either >20 µm or >40 µm.   We assumed that this size class extends to an upper limit of 200-µm cells, because many common protists (e.g., diatoms, dinoflagellates, and ciliates) seen in these samples can reach this size.  However, we acknowledge that epifluorescence microscopy likely misses many <200-µm metazoan zooplankton (e.g., appendicularians and copepod nauplii that are likely common in all study regions) as well as fragile rhizarians (that are known to be common and contribute to export in the CCE region, Gutierrez-Rodriguez et al. 2019).  Our estimate of the biomass of this size class is thus likely an underestimate.  III) The upper limit of the >5-mm mesozooplankton size class is also unknown.  We consistently treated this size class as encompassing organisms from 5 – 50 mm because 50 mm was a reasonable estimate for the upper limit of organisms typically collected in this size class.  However, functionally this class includes all >5 mm taxa that were present and did not avoid the net.  For instance, the “5 – 50 mm” size class often included ~100 mm salps in the SalpPOOP study and 50 – 200 mm pyrosome colonies in the CCE.  While it might have been most appropriate to remove all >50 mm organisms from this size class, this was not possible as the proportion of the biomass contained in >50 mm organisms was not included in datasets.  Furthermore, since our goal was to estimate the slope of the plankton size spectrum, the exclusion of all large mesozooplankton would bias our results.  We thus consider it most appropriate to sum all >5-mm taxa into a single size class and use a typical maximum size (50 mm) as the assumed upper limit of the bin. 

We determined the average euphotic zone biomass in each size bin.  For microbial populations, we vertically-integrated the biomass profiles from 6 – 8 depths through the euphotic zone.  We then divided by the depth of the deepest sample (which was always near the base of the euphotic zone) to determine an average volumetric carbon biomass (mmol C m-3).  Multiple profiles per Lagrangian experiment were averaged.  For mesozooplankton size classes, volumetric carbon biomass was determined by dividing the net-tow biomass by the volume filtered (determined using a flow meter attached to the net frame).  For each Lagrangian experiment, we computed daytime and nighttime average biomasses and then took the average of these two values to get a day-night mean estimate of volumetric carbon biomass.  Individual microbial size classes thus typically incorporated ~24 distinct measurements (6 depths × 4 days for one Lagrangian experiment), while zooplankton size classes typically incorporated 8 distinct measurements (~2 day-night tows per day × 4 days).  We believe this results in very robust estimates of the NBSS for these programs.  For the station ALOHA samples, results are typically derived from a single profile of microbial measurements (Pasulka et al. 2013) and three day-night pairs of zooplankton net tows and hence should be assumed to have greater uncertainty.

Loaded the submitted Excel spreadsheet Supp Table 1_BCO-DMO.xlsx into the BCO-DMO data processor Laminar.

The original Date column contains a mixed format of data and time where some entries don’t have a time and some entries have an abbreviated month rather than a number.

Split the date and time values into 2 new columns to reformat. Not all entries have a time value and the submitter requested the Time column be removed and only the Date values be kept.

Inside the new Date column, converted 3 letter month abbreviations in the dates to numeric values.

The year is a two digit year with a known century of 2000, so the two digit year was prefixed with ‘20’ to create a 4 digit year.

Reformatted new dates into the ISO format of %Y-%m-%d.

Removed the original date column.

Renamed the column ‘Cruise / Cycle ID’ to ‘Cruise_ID_or_Cycle_ID’.

Renamed the fields using the BCO-DMO naming convention of no spaces or punctuation marks and with no numbers at the front of a parameter name. Spaces were replaced with underscores.

Saved the final table to 924554_v1_plankton_biomass.csv.

Checked the bacteria names in the submitted text matched the World Register of Marine Species (WoRMS) website.

NSF Award Abstract:
Salps are unique open-ocean animals that range in size from a few millimeters to greater than twenty centimeters, have a gelatinous (jelly-like) body, and can form long chains of many connected individuals. These oceanic organisms act as oceanic vacuum cleaners, having incredibly high feeding rates on phytoplankton and, unusual for consumers of their size, smaller bacteria-sized prey. This rapid feeding and the salps' tendency to form dense blooms, allows them move substantial amounts of prey carbon from the surface into the deep ocean, leading to carbon dioxide removal from the atmosphere. However, salps are often considered a trophic dead-end, rather than a link, in the food web due to the assumption that they themselves are not consumed, since their gelatinous bodies are less nutritious than co-occurring crustacean prey. Along with this, salp populations are hypothesized to be increasing due to climate change. This proposal addresses these questions: 1) Do salps compete primarily with crustaceans (as in the prevailing paradigm) or are they competitors of single-celled protists, which are the dominant grazers of small phytoplankton? 2) Do salp blooms increase the efficiency of food-web pathways from tiny phytoplankton to fisheries production in nutrient-poor ocean regions?

This project will support the interdisciplinary education of a graduate student who will learn modeling and laboratory techniques in the fields of biological and chemical oceanography and stimulate international collaborations between scientists in the United States and New Zealand. Additionally, several Education and Outreach initiatives are planned, including development of a week-long immersive high school class in biological oceanography, and education modules that will serve the "scientists-in-the schools" program in Tallahassee, FL.

It is commonly assumed that salps are a trophic sink. However, this idea was developed before the discovery that protists (rather than crustaceans) are the dominant grazers in the open ocean and was biased by the difficulty of recognizing gelatinous salps in fish guts. More recent studies show that salps are found in guts of a diverse group of fish and seabirds and are a readily available prey source when crustacean abundance is low. This proposal seeks to quantify food web flows through contrasting salp-dominated and salp-absent water parcels near the Chatham Rise off western New Zealand where salp blooms are a predictable phenomenon. The proposal will leverage previously obtained data on salp abundance, bulk grazing impact, and biogeochemical significance during Lagrangian experiments conducted by New Zealand-based collaborators. The proposal will determine 1) taxon- and size-specific phytoplankton growth rate measurements, 2) taxon- and size-specific protozoan and salp grazing rate measurements, 3) compound specific isotopic analysis of the amino acids of mesozooplankton to quantify the trophic position of salps, hyperiid amphipods, and other crustaceans, 4) sediment traps to quantify zooplankton carcass sinking rates, and 5) linear inverse ecosystem modeling syntheses. Secondary production and trophic flows from this well-constrained ecosystem model will be compared to crustacean-dominated and microbial loop-dominated ecosystems in similarly characterized regions (California Current, Costa Rica Dome, and Gulf of Mexico).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.